Electronic ignition system



July 2, 1968 A. G. HUFTON ELECTRONIC IGNITION SYSTEM Filed April 13, 1966 FIG. 2

T CENTER POST 0F \SDISTRIBUTOR DC TO DC "7 CONV I3 25 FIG. 1

FIG. 5

FIG.3

BIAS LEVEL FOR CONDUCT- ION TIME

T|ME

FIG. 6

S mm ,w A WW4 H T R M M B am m F United States Patent 3,390,669 ELEGTRONIC IGNITION SYSTEM Arthur G. Hutton, Elk Grove Village, Ill., assignor to Motorola, Inc., Franklin Iark, 111., a corporation of Illinois Filed Apr. 13, 1966, Ser. No. 542,337 11 Claims. (Cl. 123-148) ABSTRACT OF THE DISCLOSURE An ignition system including a magnetic pickup operable with the distributor breaker cam to provide timing pulses to a semiconductor circuit which produces firing pulses. The semiconductor circuit includes a variable impedance coupling circuit having a resistor with a transistor thereacross which is cut off as the frequency of the pulses increases to increase the impedance, and a damped oscillator for producing a single firing pulse in response to each timing pulse.

This invention relates to ignition systems for internal combustion engines, and more particularly to ignition systems wherein timing pulses are produced by a magnetic device synchronized with the engine.

Ignition systems used with internal combustion engines generally include some type of circuitry for producing high energy voltage pulses for igniting the fuel in the cylinders of the engine. These high voltage or ignition pulses may be produced by the interruption of current flowing in an ignition coil or may be produced by a rapid discharge of current through the ignition coil from an energy storage device (capacitor discharge). In either case, the ignition pulses must be synchronized in some manner with the operation of the internal combustion engine.

In the so called Kettering type of ignition system, which has been in widespread use over many years, the high voltage ignition pulses are produced by the interruption of current through an ignition coil by opening and closing a pair of mechanical breaker points or contacts, through the action of a cam mounted on the shaft of the distributor. It has been proposed to avoid using cam actuated mechanical breaker contacts to break the coil current, as such contacts become dirty and worn with use and must be replaced.

Certain types of ignition systems using magnetic pickup devices have been designed for use in place of the mechanical cam actuated breaker contact systems. Such a system is shown in Patent No. 3,203,412, issued Aug. 31, 1965, and assigned to the assignee of the present invention. In such an ignition system, a transistor circuit interrupts the coil current in response to timing pulses supplied to the transistor circuit from a magnetic pickup device. The magnetic pickup device can also be used to supply timing pulses to control the discharge of a capacitor in a capacitor discharge type ignition system. In the latter case, the timing pulses produced by the pickup device may be used to operate a transistor circuit which produces firing pulses to trigger the capacitor discharge.

A magnetic pickup device, when used with a transistor circuit of either of the above described types, may cause diificulties due to the occurrence of a phase lag in the timing pulses produced by the device as the frequency of pulses increases. This is because the transistor, being a current operated device, will be susceptible to timing error due to the phase lag in the current. Furthermore, in a capacitor discharge system it may be difficult to obtain timing pulses of sufiiciently high voltage to cause the transistor circuit to produce large enough firing pulses when the magnetic pickup device is operating at low speeds or at low ambient temperatures. Finally, many magnetic pickup devices have been found unsatisfactory for incorporation in existing ignition systems as they require relatively extensive modification of the distributor which includes a cam for operating mechanical breaker points. This makes ignition systems using magnetic pickup devices relatively expensive and impractical for installation in existing systems.

An object of this invention is to provide an improved magnetic pickup device for use in an ignition system, which device may be readily incorporated in the housing of a distributor of the type having a cam for operating mechanical breaker points.

A further object of this invention is to provide an ignition system utilizing a magnetic pickup device and which minimizes current phase lag in the timing pulses produced by the device as the frequency of the pulses is increased.

Another object of the invention is to provide an ignition system utilizing a magnetic pickup device and a transistor circuit wherein voltage pulses of a relatively high value are produced despite low speed operation of the pickup device.

A still further object of the invention is to provide an ignition system which may be readily substituted for an existing system using cam operated-mechanical breaker contacts, and which is not susceptible to current phase lag, and which operates satisfactorily at slow speeds and low temperatures.

A feature of the invention is the provision of an ignition system including a coupling circuit connected to a magnetic pickup device and which includes variable impedance means responsive to the trigger pulses produced by the device to vary the load presented to the device by the coupling circuit in inverse proportion to the frequency of the pulses applied to the coupling circuit.

Another feature of the invention is the provision of a firing circuit connecting a magnetic pickup device to an ignition circuit, which firing circuit operates as a damped oscillator to produce a single firing pulse for the firing circuit in response to each timing pulse supplied thereto from the pickup device.

Still another feature of the invention is the provision, in a distributor, of a magnetic pickup device having an elongated pole piece disposed perpendicular to the axis of rotation of the breaker cam with one end of the pole piece disposed adjacent the periphery of the cam and with a permanent magnet having one pole disposed adjacent the other end of the pole piece and having the opposite pole disposed such that an air return flux path exists between the opposite pole and the cam.

In the drawings:

FIG. 1 is a schematic diagram of an ignition system including a magnetic pickup device in the distributor, the distributor being shown in fragmentary view;

FIG. 2 is a full section view of the distributor taken along the line 22 of FIG. 1;

FIG. 3 is a graph illustrating the change in flux density with cam rotation in the ignition system pickup device of FIGS. 1 and 2;

FIG. 4 is a graph illustrating the voltage output of the pickup device;

FIG. 5 is a graph illustrating the base voltage on the first transistor of the ignition system of FIG. 1;

FIG. 6 is a graph illustrating the voltage at the positive end of the coupling transformer of the ignition system of FIG. 1;

FIG. 7 is a schematic diagram of the equivalent circuit for the pickup device and coupling circuitry associated therewith, in the ignition system of FIG. 1; and

FIG. 8 is a vector diagram illustrating the operation of the circuit of FIG. 7.

In accordance with the invention, an ignition system for an internal combustion engine includes a magnetic pickup device operable in synchronism with the internal combustion engine to produce timing pulses. A circuit which is responsive to timing pulses applied thereto to produce ignition pulses for the internal combustion engine, is connected to the magnetic pickup device by a coupling circuit. The coupling circuit varies its impedance in response to the trigger pulses applied to the coupling circuit to vary the load presented to the magnetic pickup device by the coupling circuit in inverse proportion to the frequency of the trigger pulses applied to the coupling circuit.

In one form of the invention, the circuit for producing ignition pulses comprises an ignition circuit which is responsive to firing pulses applied thereto to produce the ignition pulses. A firing circuit connects the pickup device to the ignition circuit to supply the firing pulses thereto. The firing circuit includes a coupling circuit which connects it to the magnetic pickup device, and also includes a damped oscillator therein producing a single firing pulse for the firing circuit in response to each timing pulse applied through the coupling circuit from the pickup device. The magnetic pickup device used with the foregoing ignition system may be of a form mounted in a distributor having a polygonal breaker cam rotatable in synchronism with the engine. This form of the pickup device includes an elongated pole piece having first and second ends. The pole piece is mounted in the distributor perpendicular to the axis of rotation of the cam and has its first end disposed adjacent the periphery of the cam. A permanent magnet having one pole disposed adjacent the second end of the pole piece has its opposite pole disposed such that an air return flux path exists between the opposite pole and the cam. Thus, the flux through the pole piece increases and decreases as the breaker cam rotates with respect thereto. A winding surrounds the pole piece between the first and second ends thereof and is responsive to the variation of flux therethrough to provide timing pulses for the ignition system.

Referring now more particularly to the drawing, FIG. 1 shows the invention used in connection with an ignition system of the capacitor discharge type. An ignition capacitor 11 is charged through DC to DC converter 12 and diode 13 to a very high voltage. When the semiconductor cont-rolled rectifier 14 is triggered on by means of a pulse applied to the gate thereof, the capacitor 11 dis-charges through the primary portion of high voltage ignition transformer or coil 15. This produces a very high voltage in the secondary of ignition coil 15, which is applied to the center post of the distributor. This is coupled by the distributor to the spark producing devices of the cylinders of the engine in a well known manner for igniting the fuel in the cylinders. A diode 16 is connected in reverse polarity across rectifier 14 to damp reverse voltage transients produced in the coil 15.

Semiconductor controlled rectifier 14 is triggered by pulses produced in synchronism with the operation of the internal combustion engine. A magnetic pickup device 20 is provided in the distributor of the ignition system and includes a magnetic structure 21 having a pole piece 22 which is positioned adjacent the breaker cam 25. A coil 26 on the magnetic structure produces a voltage wave which is applied to the pickup output point 30.

The voltage at the pickup output point 30 is converted to a pulse wave for triggering the semiconductor controlled rectifier 14 by a circuit including transistors 31, 32 and 33. Bias potential is provided for the transistors by a voltage divider connected from the DC terminal 34, and including resistor 35 and diodes 36, 37, 38 and 39.

Transistor 31 has an emitter electrode connected to point 3% and a base electrode connected through capacitor 40 to point 30. The collector electrode of transistor 31 is connected through diode 41 and resistor 42 t the junclion between diodes 37 and 38, and the base electrode is connected through resistor 43 to the junction between A diodes 38 and 39, so that in the quiescent state transistor 31 is biased to be normally conducting.

The pickup output point 30 is connected through resistor 45 and the parallel network of diode 41 and capacitor 46 to the base of transistor 32. Thus, resistor 45 is connected in shunt with the emitter-collector path of transistor 31 between point 30 and the parallel network 41, 46. A diode 47 connects the junction between resistors 45 and diode 41 to ground.

When a signal in the form of a positive voltage is applied to the output point 30- by the magnetic pickup device 20, capacitor 46 applies a positive voltage to the base of transistor 32, clue to conduction through resistor 45 and through transistor 31 when it is conducting. This latter fact depends upon the bias at which transistor 31 is operated and this is made variable in accordance with the invention, as will be explained subsequently.

Transistor 32 has its base electrode connected through resistor 42 to the junction between diodes 37 and 38, and its collector electrode connected through resistor 49 to the junction betwen diodes 36 and 37. Transistor 32 is biased to the threshold of conduction so that this transistor is normally oif. When the potential applied through re sistor 45 and/or transistor 31 to the 'base electrode of transistor 32 becomes positive, this drives transistor 32 into conduction.

The collector of transistor 32 is connected to the base electrode of transistor 33 through the parallel connection of resistor 51 and capacitor 52. The emitter and collector electrode path of transistor 33 is connected in series with the primary Winding 53a of transformer 53, and through resistor 54 to the junction on the voltage divider between resistor 35 and diode 36. Transistor 33 is biased to be conductive in the quiescent state of the system. Diode 55 is connected across the primary winding of transformer 53 to damp out transients therein. A Zener diode 56 is connected across the collector and emitter electrodes of transistor 33 to protect the transistor from breakdown due to high reverse transient voltages which may be developed in primary winding of transformer 53. The secondary winding 53b of transformer 53 is connected to the gate of the semiconductor controlled rectifier 14.

When transistor 32 is rendered conducting by the voltage from the pickup 20, this tends to turn transistor 33 oflF. The reduction in current through the primary winding of transformer 53 causes a damped oscillation of approximately the natural frequency of the primary winding (for example 40 kc.), which may extend for a relatively long duration (50 microseconds). This raises the voltage at the supply potential end of the primary winding above the applied potential voltage (see FIG. 6). This voltage is fed back through resistor 57 to the base of transistor 32, and provides a fast positive going voltage at the base which forces the transistor 32 to positively conduct. This, in turn, turns off transistor 33 very rapidly (for example 2.5 microseconds).

The voltage on the base of transistor 31 is shown in FIG. 5. The fast rise time of this pulse produces a rapid break of current in transformer 53 and consequently induces a very high voltage in the secondary winding 5312. This occurs despite a very low pulse applied to the base of transistor 32 by the pickup device 20.

The natural resonance frequency of winding 53a is selected to be substantially removed from the time constant of the circuitry connected thereto, such that the fast switch off and on of transistor 33 at the resonant frequency of winding 53a adds very little to the energy stored in the winding. Since switching can only take place while energy is stored in the winding, transistor 33 is held in the off state until the voltage pulse from the magnetic pickup device 20 is insuflicient to maintain the transistor 32 in conduction. FIGS. 5 and 6 show the operation of these respective voltages and it will be seen that irrespective of the voltage produced in pickup 20,

the voltage pulses in the primary winding 53a are of substantially constant energy.

Referring to FIGS. 1 and 2, the distributor in which pickup device 20 is mounted includes a housing 71 and a cap 72. A distributor shaft 73 extends upwardly into the housing and drives the drive plate 75. Drive plate 75 is connected through the usual spring biased flyweights 77 and drive pins 78 to a centrifugal advance plate 79. Advance plate 79 drives the rotor shaft 81 upon which the rotor 83 is mounted. Rotor 83 carries the moving contact of the distributor and the fixed contacts of the distributor extend downwardly in the interior of cap 72 as is well known in the art. Rotor shaft 8 1 carries the cam 25 which is of the type used to operate mechanical breaker points. The periphery of such a cam comprises a plurality of substantially planar surfaces which intersect in lines extending parallel with the axis of rotation of the cam. As may be seen from FIG. 1, this forms a plurality of points 25:: on the cam 25. J

The configuration 0f the magnetic pickup device 20 is shown in FIGS. 1 and 2. The device includes a single core 21 which corresponds substantially with the height of the distributor cam 25. A winding 26 surrounds the core 21 and one end of the winding is connected to ground or reference potential, and the other end to the output point 30. The core 21 is secured through a piece of non-magnetic material 63 to the vacuum advance plate 88 of the distributor. A pair of permanent magnets 65 and 66 are disposed on either side of the core 21 at the end thereof opposite to the end 22 adjacent cam 25. Magnets 65 and 66 have identical poles (north in the drawing) adjacent the core 21 and have their opposite poles disposed such that an air return path exists between these poles and the cam 25. The whole face of each of the magnets 65 and 66 is embraced by the pole piece without any narrowing between the magnet and the gap between the pole piece and the cam which would decrease the value of the reluctance in the flux path. By removing the conventional mechanical breaker contacts and substituting a pickup device of this type, this ignition system may be readily incorporated in a conventional distributor in an existing ignition system.

As the cam 25 rotates proximate the end 22 of core 21, the gap between the cam and the pole end varies. This produces a variation in flux as shown in FIG. 3, which produces timing voltage pulses in the coil 26 as shown in FIG. 4. These pulses are connected as before described to the transistor 32 for triggering the ignition system in synchronism with the engine 10. It will be seen that the greater the rotational speed of the cam, the greater the rate of change of flux and hence the greater the voltage pulse produced. Triggering of transistor 32, however, takes place at the same voltage regardless of speed.

A phase shift exists between the triggering position of the cam and the current flowing in the coupling circuit. This phase shift will vary with varying current. As the transistor is a current operating device, any change in the phase angle of the current will affect the triggering time of transistor 32. FIG. 7 shows an equivalent circuit of the magnetic pickup device 20 with its external load where R and X represent the leakage resistance and reactance of coil 26. FIG. 8 is a phase diagram showing the phase relationship of the various components found in FIG. 7. It will be seen that the voltage E (the theoretical voltage across coil 26) lags the magnetic flux through core 21 by 90". Due to leakage reactance, the current through the circuit I lags the voltage E by an angle [3, and because of the capacitor 46 in the load, V (the actual voltage across coil 26) lags the current I by an angle a. Without a capacitor, V would assume a position V As the capacitor is a fixed quantity at the triggering point, it has little affect in the position of the current vector relative to the flux shown by angle 9. However, the component IX can cause a change in the angle 0,

if this change is not accompanied by a comparable change in the EMF vector E. This is the case when the frequency and current increase at the same time and when a fixed load is used. It is considered that this phase shift is the major cause of spark retardation with increase in distributor cam speed for various types of magnetic pickup de vices used with transistor circuitry.

In accordance with the invention, load current I (FIG. 8) is limited (by transistor 31 and resistor 45) as the distributor cam speed is increased in order to overcome the phase shift previously discussed. At distributor cam rotational speeds of 0 to 500 rpm, transistor 31 is conducting and the voltage developed across the rail 26 is directly applied across diode 47, and across capacitor 49 in series with the base-emitter circuit of transistor 32. At cam speeds greater than 500 rpm, transistor 31 is progressively turned off due to the shorting action of capacitor 40. At a speed of approximately 2500 r.p.m., the only path for pickup current is through resistor 45. Thus, by utilizing transistor 31 and resistor 45 as shown, a variable impedance is presented to the pulses from the pickup device 20 with variation in frequency. As this impedance increases with increasing frequency, the load ing of the pickup device 20 is reduced accordingly. This minimizes the drop V due to the leakage reactance and resistance. The higher impedance is easily overcome by the increase in magnitude of voltage pulses produced by the coil due to increased speed of operation. There is still, of course, some phase lag but it is effectively minimized to a point where it does not detrimentally affect the operation of the ignition system.

The circuit described provides accurate triggering of the automobile ignition system at all engine speeds, with timing information at least equally as good as conventional mechanical breaker points. Triggering is readily obtained at battery voltages from 6 volts to in excess of 16 volts, and at temperatures between approximately -40 F. and 300 F. It may therefore be seen that the invention provides an improved ignition system for an internal combustion engine and an improved magnetic pickup device for use therewith.

I claim:

1. A magnetic pickup device for use in an internal combustion engine ignition system having a distributor with a polygonal breaker cam rotatable in synchronism with the engine, said pickup device including in combination, an elongated pole piece having first and second ends, means for mounting said pole piece in the distributor with said first end disposed adjacent the periphery of the cam and substantially parallel to the axis of rotation of the cam, permanent magnet means including first and second permanent magnets having like magnetic poles connected to said pole piece so that the magnetic flux produced by said magnets combines in said pole piece and extends through an air gap to the cam, whereby the flux through said pole piece increases and decreases as the breaker cam rotates with respect thereto, and winding means surrounding said pole piece between said first and second ends thereof and being responsive to the variation of flux therethrough to provide timing pulses for the ignition system.

2. A magnetic pickup device in accordance with claim 1 wherein said permanent magnet means includes a pair of permanent magnets each having identical poles disposed adjacent said second end of said pole piece and having their opposite poles disposed such that an air return flux path exists between said opposite pole and the cam.

3. A magnetic pickup device in accordance with claim 2 for use with a distributor including a vacuum advance plate, and which includes means for mounting said pole piece to the advance plate of the distributor, with said pole piece having a dimension parallel to the axis of rotation of said cam which corresponds substantially with the dimension of said cam parallel to the axis of rotation thereof.

4. A pulsing circuit for an ignition system for an internal combusion engine which includes an ignition circuit responsive to firing pulses applied thereto to produce ignition in the internal combusion engine, said pulsing circuit including in combination, a magnetic pickup device operable in synchronism with the internal combustion engine to produce timing pulses, and a coupling circuit connected to said magnetic pickup device for applying firing pulses to the ignition circuit, said coupling circuit including variable impedance means responsive to the pulses applied thereto by said device to provide an impedance varying in the same sense as the frequency of the timing pulses applied thereto, the increasing impedance of said variable impedance means of said coupling circuit with increasing frequency acting to reduce the current applied through said coupling circuit to thereby minimize the current phase lag in the firing pulses applied to the ignition circuit.

5. A pulsing circuit in accordance with claim 4 wherein said variable impedance means includes parallel connected transistor means and resistance means, and means connected to said transistor means and responsive to the timing pulses applied to said coupling circuit to bias said transistor means to vary the conduction thereof and thereby vary the impedance of said variable impedance means.

6. A pulsing circuit in accordance with claim 4 wherein said variable impedance means includes a transistor having a primary current path and a control current path, and resistor means connected in shunt with said primary current path, said coupling circuit further including capacitor means connected to said magnetic pickup device and connected in said control current path of said transistor, said capacitor means being responsive to the frequency of the timing pulses applied thereto from said magnetic pickup device to reduce the conduction of said transistor with increasing frequency so that the effective impedance of said variable impedance means increases.

7. The combination of claim 6 further including damped oscillator means connecting said coupling circuit to the ignition circuit, said damped oscillator means applying to the ignition circuit in response to each timing pulse a single firing pulse having substantially constant energy which is independent of the magnitude of such timing pulse.

8. An ignition system for an internal combustion engine including in combination, a magnetic pickup device operable in synchronism with the internal combustion engine to produce timing pulses, an ignition circuit responsive to firing pulses applied thereto produce ignition pulses for an internal combustion engine, and a firing circuit connected between said magnetic pickup device and said ignition circuit and including first and second transistors, said first transistor being rendered conducting to cause said firing circuit to apply a firing pulse to said ignition circuit, means connecting said second transistor between said pickup device and said first transistor and providing a bias to said second transistor to render the same conductive to apply timing pulses to said first transistor, said means including capacitor means connected to said pickup device and to said second transistor to alter the bias thereon, said capacitor means being responsive to timing pulses of a predetermined frequency to provide a bias to cut ofi said second transistor, and further means coupling said pickup device to said first transistor for applying timing pulses thereto.

9. An ignition system in accordance with claim 8 wherein said firing circuit includes a third transistor having a primary current path and a control current path, transformer means series connected with the primary current path of said third transistor and coupling said firing circuit to said ignition circuit, and feedback means including said transformer means connecting said primary current path of said third transistor to said control current path thereof and having a resonant frequency substaniially different from the resonant frequency of said transformer to clamp oscillations therein after a single firing pulse is produced, said firing circuit providing a substantially constant energy firing pulse in response to each timing pulse applied thereto from said pickup device which is independent of the magnitude of said timing pulse.

10. An ignition system in accordance with claim 8 wherein said firing circuit includes a third transistor connected in cascade with said first transistor, means for biasing said first transistor normally off and for biasing said third transistor normally on, said first transistor being conductive to cut oif said third transistor, a transformer series connected with the emitter to collector path of said third transistor and coupling said third transistor to said ignition circuit for applying firing pulses thereto in response to cut off of said third transistor by conduction of said first transistor, feedback resistance means connecting the primary winding of said transformer with the base portion of said first transistor and forming an oscillating circuit with said primary winding and said first and third transistors, said oscillating circuit having a resonant frequency substantially diiferent from the resonant frequency of said transformer to damp oscillations therein, said transformer supplying substantially constant energy firing pulses to said ignition circuit which are independent of the magnitude of said timing pulses.

11. An ignition system in accordance with claim 8 wherein said magnetic pickup device includes a distributor with a polygonal breaker cam rotatable in synchronism with the engine, an elongated pole piece having first and second ends, means for mounting said pole piece in the distributor perpendicular to the axis of rotation of said cam and with said first end disposed adjacent the periphery of said cam, a permanent magnet having one pole disposed adjacent said second end of said pole piece and having the opposite pole disposed such that an air return flux path exists between said opposite pole and said cam, whereby the flux through said pole piece increases and decreases as the breaker cam rotates with respect thereto, and Winding means surrounding said pole piece between said first and second ends thereof and being responsive to the variation of iiux therethrough to provide timing pulses.

References Cited UNITED STATES PATENTS 2,980,093 4/ 1961 Short. 3,131,327 4/1964 Quinn. 3,139,876 7/1964 Jukes. 3,196,313 7/1965 Quinn. 3,238,416 3/1966 Huntzinger et al. 3,291,108 12/ 1966 Schneider et al.

LAURENCE M. GOODRIDGE, Primary Examiner. 

